The Japan Islands, a small island chain on the western rim of the circum-Pacific region, have experienced several cultural contacts and human migrations from northern and eastern continental Asia. In this study, craniometric diversification of Asian peoples was assessed using the R-matrix method based on 21 metric traits in 25 representative male and female samples of prehistoric and modern northeastern and eastern Asians, including inhabitants of the Japan Islands. The prehistoric series show, in general, greater observed variance than expected. In the Japanese series, the greater than expected variation of the Jomon is strongly contrasted with the lower level of variability seen in the continental immigrant Yayoi, suggesting a founder effect stemming from the small population size of the initial immigrants represented by the Yayoi series. Scattergrams based on the morphological distances transformed from the R-matrix showed that the Jomon, Ainu, and prehistoric Okhotsk (northeastern immigrants to the Japan Islands) were isolated from the main eastern and northeastern Asian cluster, suggesting greater phenotypic diversity in the Japan Islanders. Despite less variability in the Yayoi series, the phenotypic contribution of the Yayoi to the main-island Japanese populations was considerable, probably because of the existence of successive immigrants after the Yayoi period and/or a higher growth rate of the Yayoi immigrant groups. An assessment of intra-regional variation of the five major Asian regional series by the R-matrix method confirmed that the Japanese series representing populations living on small islands have greater craniometric diversity than the Arctic and Coastal northeastern Asian samples.
2009 The Anthropological Society of Nippon